I do think one area 4E does fall down is the fallacy of having all monsters the party meets nearly the same level, every door nearly the same d20 roll to get open if it is part of a skill challenge.
From level 1 to 30
It's a common misconception (which I'm not accusing you of having

) that the skill DC for opening a locked door goes up as you level. It doesn't. Any given door has its own level of difficulty to open.
It's just that once you're level 20, locked doors of level 1-10 just aren't any more obstacle than unlocked ones, so you just treat them as if they weren't locked. A door of level 20 encountered by a party at level 1 is basically a wall with the promise of something interesting behind it if you come back later, rather than a door they should spend much time trying to open. The problem is, in my experience anyway, that if you put a door in, the party is convinced there's a way to get through it. If they can't force it, or pick the lock, there must be some magic, or a secret lever, or they have to knock and wait for it to be opened... I've seen people get stalled on what a DM put in as set-dressing, thinking there must be a way to get past.
Making my players roll skill checks they cannot fail (except on a 1) is a waste of my time and theirs.
Making my players roll skill checks they cannot pass is also a waste of time.
Now, it's perfectly reasonable when creating a place that you expect the players to spend a long time in, or to return to, to put in place doors that fall at the "can't possibly open right now" end. It's also reasonable to have doors that are a challenge now, but will be auto-successes later.
All of this also applies to other skill checks, of course.
Now it does not have to be this way, the DM could throw in a bunch of highly lower leveled creatures, or a higher one (and I have done this in 4E) but there is not a lot of support for this, and very few modules do this in any way.
Well, the reason there's not a lot of support for throwing in a bunch of highly lower levelled creatures in is that that's what minions are for.
Once a creature's so much lower than the party that they can't be missed, and can't hit the party, and even if they hit can't do enough damage to worry about... any reasonable party is basically going to ignore them in any fight that has real threats in it. If they're not going to actually fight the things, you may as well be treating them as a terrain feature rather than monsters.
Whereas if you instead make those creatures into minions that are within 2 or 3 levels of the party, you retain the overwhelming superiority of the PCs (one hit kills for everyone!), while making the creatures enough of a concern that the PCs might actually treat them as more than mobile terrain. (Well, if you use MM3 era minions, anyway. Earlier ones tend not to have enough going for them.)
To me, it ruins the sense of disbelief I had in most other editions. I want goblins to be low level nasties that can be ignored at a certain point. Not a 12 level spread in the MM. 3-4 is ok, for leaders, but I like monsters as more ranks of danger, stretching across 5 or so levels at max.
Luckily I can do this with monster choice as a DM but the core assumption is a bit offsetting to me.
Most goblins
are nasties that can be ignored at a certain point. It's just those few exceptional ones that are significantly better than their brethren who pop up and surprise you. It's a useful tool to have: monsters the players think are set-dressing, but who turn out to actually be threats.